Does anyone know if it is possible/desirable to run open loop at low rpm for an engine with a long duration camshaft?

 

well, sure it's possible. I'm assuming you are running $8D code (your profile says 89 vette).

There is already an closed loop enable check in the $8D code that is based off coolant temp - many folks just set it to 255 to just disable closed loop altogether and fully tune in open loop. it should be a pretty simple change to the code to make it check RPM instead of temperature - but this does require changing a few bytes in the code/.BIN.

How big of a cam are you running? What kind of problems are you running in to? Have you considered full open loop (just set the closed loop enable temp to 255)?

 

My cam has ~240@50 and 585 lift.
This cam produces an incomplete combution process at low rpm which will let a lot of air pass by the o2 creating problems in the control system.
I was thinking that in this range rather than playing alot of games it may be better just to go to open loop.
Do you know what the good and bad points would be by doing this?
I have a 1227165 6e that I am just beginning to work with but am planning on downloading from my stock memcal as a starting point.
It stumbles off idle most times and has a 160max blm in this range but pulls and sounds really good after this.

It also has a tpis minram, long tube headers, 3" y-pipe , dual exhaust, MSD, total seal rings with <5% leakdown, ati super damper, cloyes true roller, full roller rockers, 10.5:1, 3.73:1, etc.

 

You should be able to do a similar thing with the $6E. There are some documented hacks floating around - you just need to start with one of those as a base, transfer over your tables and search the code of the hack for the spot where the ECM checks the coolant temp and set it to RPM (or MPH, that works too).

But, before you dive there, you may want to look at rescaling your lower MAF tables. We had to do that on a buddy's car and that solved a lot of low rpms driveability issues.

So you have two plans of attack now.

 

Tuning for a big cam can be tricky. Mine is 242/250* and idle was a problem. I don't need to run in open loop because overlap is not too bad (about 18*), but I run it anyways. I have tuned friends cars that did need to stay in open loop to run optimal. There is no reason to run open loop under XXXXrpm, better off to run open or closed loop all the time. As some might know, I'm a big open loop fan. I doin't see any downside to running open loop unless you have a catalytic converter.

There is a few things I did to compensate for a fat cam,

First thing was to lean out idle as much as possible, aprox 15.6 is what my wideband reports. But due to reasons you discribed, the wideband readings can be skewed. I just leaned it out untill it stopped sending raw fuel through the exhaust. You know when you are on the right path because the exhaust will stink alot less.There is another condition people overlook with a fat cam. Some cams have less vacuum at idle, in turn the fuel pressure regulator will increase f/p at idle. That is another reason to lean the heck out of idle.

Second thing was to increase idle timing to 25*. That helped smooth things out really well.

Third thing is to check for idle speed errors. If the ecm senses an error in idle speed it'll throw in some spark advance or retard to compensate. Pay close attention if the corrections are helping or hurting the idle quality. If they are making idle speed suffer then remove the correction. With a big cam, the idle will vary a touch and that is why some note idle corrections. Check you scan tools "bit data" to confirm if any corrections are going on.

I think the last and final thing I can add, do not just adjust idle fuel/spark in on spot. For example, if your car idles at 900rpms and 65kpa then you'll need smooth out the surrounding entries on the table . Look at the example below....